1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to techniques for cluster-based defect detection testing for disk drives.
2. Description of the Prior Art and Related Information
Today, computers are routinely used both at work and in the home. Computers advantageously enable file sharing, the creation of electronic documents, the use of application specific software, and electronic commerce through Internet and other computer networks. Typically, each computer has a storage peripheral such as a disk drive (e.g. a hard disk drive).
Hard disk drives often employ a moveable head actuator to frequently access large amounts of data stored on the disk. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable head for reading and writing data. The HSA forms part of a servo control system that positions the head over a particular track on the disk to read or write information from and to that track, respectively.
A huge market exists for hard disk drives for mass-market computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive should be relatively inexpensive and should embody a design that is adapted for low-cost mass production, while at the same providing high data storage capacity and providing rapid access to data.
Satisfying these competing constraints of low-cost, high data storage capacity, rapid access to data and improved reliability requires innovation in each of the numerous components of the disk drive, methods of assembly, and in testing.
One way to satisfy these competing constraints is by purchasing and utilizing disks (i.e. media) at particular price points, which have some amount of expected disk defects, and margining these disk defects during verification testing of the disk drive before ultimately sending the disk drive out to a customer.
Presently, during disk drive functionality testing, before the disk drive is sent out to the customer, the disk is scanned for defects to detect defect patterns that are the result of, for example, scratches and/or thermal asperities on the disk. These defects may also be caused by head loading, head slap, and delamination. Particularly, as is presently done, the entire surface of the disk is scanned and a map or table of detected defect patterns is generated. Based on this map, radial straight line margining occurs in which defect patterns are approximated as radial straight lines on the disk and these radial straight line are stored in the memory of the disk drive as areas that are not to be used for reading or writing data to (i.e. these radial straight lines are margined).
Unfortunately, these techniques do not take into account the random nature that characterizes the way that defects often occur on disk and the irregular shapes formed by these randomly occurring defects. Moreover, present disk defect testing techniques do not take into account the reoccurrence of cluster regions across many different disks for statistical quality control purposes. For example, the reoccurrence of particular cluster defect regions at specific areas across many different disks may indicate a problem with the assembly process or with disks being provided by a disk vendor for assembly into the disk drive.